1. Field of the Invention
The present invention relates to an apparatus and a method for correcting the shape of an inner surface of a stator which is fixed inside an inner surface of a housing of a rotating electric machine.
2. Description of the Background Art
A stator of a rotating electric machine used in a compressor of a refrigerating machine or an air conditioner, for instance, is firmly fitted inside an inner surface of a housing of the rotating electric machine by such a mating technique as shrink fitting in most cases. If the inner surface of the housing does not have a correctly shaped circular cross section, roundness of an inner surface of the stator will be impaired as a result of fitting operation, thus creating a nonuniform air gap between the inner surface of the stator and an outer surface of a rotor. This would produce such problems as an increase in operating noise of the rotating electric machine and deterioration of startup performance thereof. A Japanese Industrial Standard defines “out-of-roundness,” or a roundness error, as the amount of radial deviation of a profile of a round object from a geometrically correct circle. More exactly, a roundness error of a measured profile of an object which should ideally be round-shaped (circular or cylindrical) is expressed by a difference between the radii of two geometrically correct concentric circles one of which is inscribed in the measured profile and the other is circumscribed about the measured profile so that an area between the two circles is at a minimum.
As an example, Published Japanese Patent No. 3678102 describes a conventional approach to achieving roundness of an inner surface of a stator of a rotating electric machine provided with a stator core having a yoke portion and a tooth portion which are divided into a plurality of yoke elements and tooth elements, respectively. The approach of this Published Patent intended for use in manufacturing the rotating electric machine is to shape an inner surface of the stator core to an out-of-roundness value of 0.03 mm or less by applying a uniform stress on the stator core radially inward from an outer periphery of the stator core toward an inner periphery thereof.
The conventional approach of the aforementioned Published Patent to shaping the inner surface of the stator core to achieve an out-of-roundness value equal to or less than a specified value has a problem that this approach is not applicable to other than a stator structure in which the yoke portion and the tooth portion of the stator core are divided into a plurality of yoke elements and tooth elements, respectively.